1. Field of the Invention
The present invention relates to a roof bit drill and, more particularly, to a roof bit drill used for imparting within the roof of a mine, counter bores suitable for recessing roof mine bolts.
2. Description of Related Art
In mine work, such as coal mining, or in underground formations such as tunnels or other excavations, it is necessary to reinforce or support the roof and/or walls of the excavation to prevent rock falls or cave-ins. Among the most common means in use for such support are cable bolts or other suitable elongated members, such as rod bolts, which are inserted into bore holes and exposed to a resin mixture or anchored therein to hold a metal support or bearing plate in tight engagement with a roof or wall surface. With respect to cable bolts, a resin system introduces resin capsules or cartridges into the bore hole and then advances the cables to a blind end of the bore hole by the cable bolt backing the capsules. The spinning of the cable bolt ruptures the capsules and mixes the resin system supplied.
Each of these cable bolts or rod bolts utilize either a barrel or wedge assembly or a bolt head, respectively, to secure the metal support or bearing plate against the roof. Therefore, the barrels of the cable bolts extend into the usable walk/crawl or transportation space in a mine as defined by the distance from the floor to the ceiling of the mine tunnel. FIG. 1 depicts a prior art cable bolt including a wedge assembly 2 and a multi-strand cable 3 secured to a barrel 8 as situated with respect to a roof line in a mine. A drive head, such as a nut 9, may be attached to a free end of the cable 3. An exemplary height of the prior art barrel and wedge assembly 2 is approximately 3 inches. Accordingly, several inches (not including the thickness of the prior art bearing plate 6) of material extends below the roof line. The prior art barrel and wedge assembly 2 used in connection with typical low clearance tunnels requires that due care be exercised while moving within the tunnel, as the extending bolt head may be engaged by moving equipment or mine personnel.
FIG. 2 illustrates another prior art embodiment, wherein a countersunk recess 13, which may have a generally curved profile, such as substantially semi-spiracle, is formed through a roofline 10 into the roof 11 to accommodate a crater plate or dome plate 14 therein. The crater plate 14 includes a raised portion 16 that substantially corresponds to the shape of the countersink 13. As a result of the profile of the crater plate 14, a cable 21 or bolt may be positioned within a top portion 30a of the barrel 26 such that the cable bolt/cable rod is significantly recessed within the roof line thereby reducing the obstruction caused by this assembly. The barrel 26 of the bolt cable 21 illustrated in FIG. 2 has a bottom portion 32 which protrudes below the roof line.
However, drilling such a hole may be challenging because there are no drills known to the inventors capable of producing such a countersink and, furthermore, any drill that is capable of producing such a countersink would, in all likelihood, require accessories to collect material removed by the drill and minimize the production of dust.
FIG. 3 illustrates a drill bit tool 70 which includes a counter bore bit 72 securely fixed to a first drill shaft 74. The counter bore bit 72 is sized to create the countersink 13 (FIG. 2) to accommodate a crater plate having a corresponding shape. The counter bore bit 72 may include raised cutting surfaces or protrusions, such as ribs 73. However, this design makes no provisions for evacuating either dust produced by this operation or larger material removed during this operation.